Tree House of Horror II: A Simpsons Halloween - S3-E7
Continuity mistake: When Homer purchases the monkey's paw, you can see open desert to the right of Homer. There was a building in its place a few shots earlier. (00:02:30 - 00:03:15)
Other mistake: When The Town is singing the Christmas carol you can see Sideshow Bob, who was arrested and jailed in series 1. We know he hasn't been released, as that's a plot point over the show. (00:18:10)
Suggested correction: Maybe he was allowed to participate due to good behavior. That's a possibility.
Good behavior or not, a prison wouldn't furlough an inmate just so they could participate in a snow day.
I'm not sure if it's been discussed here or listed as a mistake. Part of the problem with "The Simpsons" and the Sideshow Bob character is that time both moves forward and doesn't move. In "A Brother From Another Series," Krusty visits the prison and tells Bob he hasn't seen him in years because Bob had been in prison all those years for his crimes. Yet Bart and Lisa are still the same age and in the same grade. Bob is also let out of prison on a work-release program in the episode.
Revealing mistake: When Homer pushes the soda vending machine next to the candy vending machine, a large scratch appears near the upper right corner of the screen. (00:04:10)
Suggested correction: This is in the questions as well. With the long amount of time the artists have to make an episode it's very hard that something like this would get by them. It's probably the device you watched it on.
Continuity mistake: In the new opening sequence, Kearney and Dolph cut off Jebbidah's head. But in the pan of the city, the head is back.
Burns Verkaufen der Kraftwerk - S3-E11
Continuity mistake: When Homer is at the vending machine, in certain shots he is wearing a tie and in others he isn't. (00:02:20)
Character mistake: Burkina Faso is listed as being among the Southern Hemisphere locations Bart called when Homer is looking over the phone bill; since Burkina Faso is completely within the Northern Hemisphere, it would have made no sense for Bart to call there.
Suggested correction: It may not make sense, but Bart isn't exactly the sharpest tool in the shed. In this same episode, he looked at his globe and thought Rand McNally was a country and was convinced by Lisa that the citizens there wear hats on their feet and that hamburgers eat people. Additionally, he could have just decided to prank call someone there if for no other reason than he thought the name of the country was funny.
Entirely possible, but since Bart had a globe right there to refer to, even someone with his limited geographical knowledge would have been able to tell that Burkina Faso is in the Northern hemisphere, unlike the other locations he did call as depicted in the montage (Antarctica, Argentina, unspecified South American nation, etc).
Homer's Triple Bypass - S4-E11
Continuity mistake: When Homer begins praying, the room is dark and there is barely any light. When the nurse shushes him, suddenly it's a lot brighter. (00:14:20)
Homer's Triple Bypass - S4-E11
Continuity mistake: When Barney and Moe visit Homer, the vase of flowers disappears and then suddenly reappears at the end of the scene. (00:16:10)
Marge vs. the Monorail - S4-E12
Other mistake: When Homer crashes his car, he just disappears when it hits the tree. (00:01:50)
Marge vs. the Monorail - S4-E12
Continuity mistake: When Grandpa Simpson stands up in The Town hall, the position and amount of paintings on the wall change several times between shots. (00:06:10)
Marge vs. the Monorail - S4-E12
Other mistake: Lanley's desk in his trailer suddenly gets brighter even though none of the lights in the trailer were turned on. (00:12:50)
Audio problem: When Patty says "Marry me Patty?" while reading Skinner's message, her mouth doesn't move.
The D'oh-cial Network - S23-E11
Continuity mistake: At one point in court while everyone is laughing, Patty's hair is colored wrong. Her hair is a similar shade of color as Rod and Todd (who are sitting next to her) rather than her own bluish grey hair.
Marge vs. the Monorail - S4-E12
Revealing mistake: When the passengers board the Monorail, Homer begins pushing two buttons. The second button he pushes is just the counter. There is no button there. (00:15:40)
Brother Can You Spare Two Dimes? - S3-E24
Other mistake: On the DVD, when Homer is sitting on the Spinemelter, he says at one point "I've tried to fill it with family, religion, community service, but those were dead ends. This card is the answer." However the subtitles say "I've tried to fill it with family, religion, but those things were dead ends. This card is the answer", leaving "community service" out.
Suggested correction: It is very common to shorten the subtitles so viewers don't have to read much.
Springfield Connection - S6-E23
Other mistake: Right before Homer draws a line between him and Marge in their bedroom, there is a weird glitch where the scene fades out a bit and back in. It almost looks like a power outage but serves no purpose. This is on the Disney+ version of the episode.
Suggested correction: It seems like it was done on purpose, as it includes the sound effect of a light bulb burning out. Clearly, it was meant to reference Hans Moleman's electric chair scene. The electric shock probably used up too much power—that's the joke.
Character mistake: When Chief Wiggum shows up to arrest Nelson during the game at the end of the episode, Bart goes with Wiggum instead while pretending to be Nelson. Even a cop as incompetent as Chief Wiggum would not have mistaken Bart for Nelson since he'd had numerous dealings with both before this episode; Wiggum may not be particularly bright, but he knows who's who in Springfield.
